Update Combustion gem

Fix compatbility with Rails 5.1.

Author: tf

activeadmin-searchable_select.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rake'
   spec.add_development_dependency 'appraisal', '~> 2.2'
   spec.add_development_dependency 'rspec-rails', '~> 3.6'
-  spec.add_development_dependency 'combustion', '~> 0.7.0'
+  spec.add_development_dependency 'combustion', '~> 1.0'
   spec.add_development_dependency 'database_cleaner', '~> 1.6'
   spec.add_development_dependency 'sqlite3', '~> 1.3'
   spec.add_development_dependency 'capybara', '~> 2.15'